The present invention relates generally to ejectable protective covers for fiber optic cable payout systems, and more particularly to ejectable lightweight foam covers for fiber optic cable payout systems for wing-mounted optically-guided glide weapons.
Many wing-mounted weapon systems, so-called smart bombs or glide weapons, are guided to their target from the launching aircraft. A common acronym for such glide weapons is GBU followed by a numerical designation, such as GBU-15 or GBU-27. GBU stands for glide-bomb unit. Glide weapons can be assembled in a variety of custom configurations to meet different requirements. Glide weapons are particularly used to deliver very large payloads precisely on target.
Glide weapons are generally configured either as optically-guided or as laser-guided. Optically-guided glide weapons have a camera in the nose of the glide weapon which sends visual images back to the launching aircraft. The pilot or weapons officer in the aircraft then sends control signals over a radio-frequency ("rf") data link to the glide weapon to guide it to its designated target.
Laser-guided glide weapons have an infrared sensor in the nose of the glide weapon. The pilot or weapons officer in the launching aircraft aims an infrared laser beam at the designated target to illuminate it. The glide weapon sensor senses the reflected laser radiation and guides the glide weapon to the illuminated target.
As indicated, most optically-guided glide weapons send and receive video and control signals by rf data links. Rf data links suffer from a number of disadvantages. Among these disadvantages are that they are subject to interference, jamming and detection.
One solution to the problems with rf data links has been to connect the launching aircraft and a launched weapon to different ends of a single strand of fiber optic cable. A dual spool fiber optic payout system dispenses a continuous length of the optical fiber simultaneously from both the aircraft and from the glide weapon. One spool is mounted inside a rear-opening payout canister mounted under a wing and the other spool is mounted inside the space at the rear of the glide weapon which otherwise would house the rf circuitry. The strand of optical fiber makes a c-shaped loop as it pays out from both canisters and drags behind the forward-moving aircraft and the dropping-away glide weapon. The optical fiber can be several kilometers in length.
Both to provide an aerodynamic shape to the rear of both the payout canister and the glide weapon, and to protect the optical fiber spools, covers are placed over the rear openings of the payout canister and the glide weapon. A reinforced section of fiberoptic cable, called a service loop, extends between the payout canister and the glide weapon and maintains the connection between the two spools while the covers are in place. Just before a glide weapon is launched, the covers must be removed so that the optical fiber can freely unspool.
Earlier attempts at making suitable covers used polyurethane foam discs which were cut free and thrust rearward by a ring-like assembly actuated by explosive driven pistons that forced the ring through the foam in cookie-cutter fashion. A lightweight foam plastic was used because pieces of such foam generally will not damage aircraft structures or aircraft engines. Unfortunately, the lightweight foam discs proved too weak to withstand the base pressure force generated by air flow. At speeds about 300 knots, chunks of foam broke off from the disc. Although the discs could have been made stronger, the cutters would then have been unable to fully penetrate the foam.
Other attempts at making suitable cover assemblies included a frangible glass dome having a bonded nylon mesh backing. A service loop connected the two covers so that when the glide weapon was launched, the service loop pulled off and shattered the glass domes. Unfortunately, in addition to other deficiencies, the cover shards and other debris can damage the delicate glass fibers.
Another attempt at making a suitable foam cover assembly uses a stronger foam cover which is fractured and pulled away by a small drogue parachute ejected by a drogue gun mounted on the side of either of the payout canister and the glide weapon. Also unfortunately, this cover assembly suffered too, in addition to other deficiencies, from the cover shards being able to damage the delicate glass fibers.
Thus it is seen that there is a need for covers for fiber optic fiber payout systems that are strong enough to withstand air flow pressures, yet which can be rapidly removed on command, and which will not on removal create broken fragments capable of damaging aircraft structures and, more importantly, the optical fibers.
It is, therefore, a principal object of the present invention to provide an ejectable, lightweight foam cover assembly for a fiber optic cable payout system that ejects quickly on command and without broken fragments capable of damaging the glass fibers.
It is a feature of the present invention that its covers can be removed for inspection, servicing or other reasons without disturbing the installation or rigging of the cutter mechanism.
It is an advantage of the present invention that it uses readily available low cost components in a simple and straightforward manner to make an inexpensive ejectable cover assembly.
It is another advantage of the present invention that it permits last minute installation of its pyrotechnic cutter mechanism where explosive hazard rules apply.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.